1. Field of the Invention
The present invention relates to a method and/or system and/or system units and/a computer program product which are usable for attaching a mobile unit to a cellular wireless communication network. In particular, the present invention relates to method and/or system and/or system units and/a computer program product, which minimize the L3 or IP signaling load during attachment or update procedures to the cellular wireless communication network.
2. Description of the Prior Art
Recently, development of communication networks has made considerable progress. Among such communication networks, there is an increasing number of communication networks supporting mobility of the users having subscribed to the networks. A user is represented by a terminal unit or terminal node he uses for communication with a communication partner unit or node. Note that in general a communication partner node is of the same or a similar type than a terminal node, while “partner node” has only been chosen to illustrate that this is the destination or called node in communication. A terminal node/communication partner node may for example be a mobile phone, mobile laptop computer, a personal digital assistant (PDA) or the like. Nevertheless, a called communication partner node may also be a fixed terminal such as a personal computer PC or the like.
Currently, 3rd generation communication networks, e.g. the Universal Mobile Telecommunication System (UMTS), are under development in 3rd Generation Partnership Project (3GPP). In general, UMTS networks includes a core network, Universal Terrestrial Radio Access (UTRA) network (UTRAN), and user equipment (i.e. user terminal units). The UTRAN provides interfaces to the core network and radio interfaces to the user equipment. As commonly known, protocols used for these interfaces are arranged into so-called layers. For example, the radio (L2) interface protocol architecture comprises a data link layer comprising e.g. medium access control (MAC) and radio link control (RLC) sublayers, and radio resource control (RRC). Furthermore, also a network layer is provided. The architecture, design as well as the used protocols of the UMTS are commonly known to those skilled in the art and will thus not be described in further detail herein.
With the increasing spreading and acceptance of the Internet, a harmonization of communication networks arises in that communication networks, in particular wireless communication networks, tend to be compatible with the Internet. Thus there is a tendency to adopt the Internet Protocol IP also in communication networks other than the Internet. IP is a packet based protocol type which allows transmitting data via the network in so-called packets comprising a header (including routing information) and a payload. In the case of mobility supporting communication networks, IP is adopted in a mobility supporting version still compatible with IP “as such”. For example, Mobile IPv4, Mobile IPv6 or Cellular IP protocol version exist.
Mobile IP specifications and definitions of common terms in this technical field can be found under http://www.ietf.org, retrieved from the Internet on Aug. 8, 2002.
There is developed a variety of wireless communication networks which support IP based communication, i.e. packet-switched networks supporting mobility of the users, such as GPRS, UMTS, Mobile IP (MIP) or the like.
In wireless cellular networks, user terminal units are able to perform communications with each other (for example within the same wireless cellular communication network) or with corresponding terminals of other networks (for example wired LANs, WLANs, fixed or mobile cellular communication networks and the like) via corresponding communication protocols. The general architecture of a wireless cellular network, for example IPv6 based, is commonly known and thus described only shortly. The key elements of a cellular access network are the user terminal units or nodes and cellular access points (CAP) with which the user terminal communicates over a wireless communication interface, e.g. radio based. A cellular access point (also referred to as base station) covers a specific area, which is referred to hereinafter as a cell. The size of a cell may vary in dependence of the environment, network operator specifications, number of associated subscribers and the like. The CAP is adapted to control communications of the user terminals within this cell, for example, by allocating frequency channels, establishing connections for the user terminals, forwarding data and the like. A user terminal is normally associated with one access point, which is referred to hereinafter as the serving CAP. A cellular access point can be associated to one or more access routers AR which routes the transmitted data via the cellular access points to and from the terminal node. Via a distribution network to which the cellular access points may be connected via the access router, communication connections between different cellular access networks or external networks (e.g. fixed networks, mobile telecommunications networks such as GSM, UMTS, WLAN and the like) can be established for a user terminal. Normally, for the communication control, the user terminal may be attached to the corresponding serving CAP via a L2 protocol and to the access router via a L3 or IP protocol.
For forwarding correctly data to and from the (mobile) user terminal, it is necessary that the network knows where the user terminal is located in the network. For this purpose, the user terminal is provided with addresses received by the respective network elements, such as the associated access point, the attached access router and the like. The addresses are registered, for example, in the home agent (HA) of the user terminal's home site. When the mobile user terminal is moved to another cell (i.e. another access point coverage area) it receives a new temporarily address which is called the Care-of-Address (CoA). When the user terminal knows the new CoA, it performs a so-called binding update procedure, e.g. a Mobile IPv6 binding update, with a corresponding network registering element, for example, with its HA. By means of this the CoA is mapped to the “permanent” address of the user terminal so as to ensure the reachability of the user terminal in the network.
A further development in the field of IP based communication networks is known as Hierarchical Mobile IP (HMIP). In this solution, a further network element is provided which is called Mobile Anchor Point (MAP). This MAP is used as a mobility agent for supporting mobility management of the user terminal in the network, e.g. in case of handovers.
In IP based communication networks, in particular in an IPv6 based network, a procedure known as Neighbor Discovery is performed. Neighbor Discovery is a commonly known concept and is described in further detail, for example, in the Internet Engineering Task Force (IETF) Requests For Comments (RFC) 1970 and 2461. In short, nodes (hosts and routers) use Neighbor Discovery to determine the link-layer addresses for neighbors known to reside on attached links and to quickly purge cached values that become invalid. Hosts also use Neighbor Discovery to find neighboring routers that are willing to forward packets on their behalf. Finally, nodes use the protocol to actively keep track of which neighbors are reachable and which are not, and to detect changed link-layer addresses. When a router or the path to a router fails, a host actively searches for functioning alternates.
According to the IPv6 Neighbor Discovery, the AR sends periodic Router Advertisements via the access points to user terminals, which are also designated as mobile nodes MN. That means, routers advertise their presence together with various link and Internet parameters periodically (or in response to a Router Solicitation message). The Router Advertisements comprise prefixes that are used, e.g., for on-link determination and/or address configuration.
The MN listens to the Router Advertisements. In the case that a new prefix is advertised, the MN determines that the network layer attachment has changed (i.e. the attachment to the AR) and computes a new CoA based on the new AR prefix (from the new AR) and then performs MIPv6 binding procedures.
However, IPv6 Neighbor Discovery, as well as MIPv6 procedures in general, affects spectrum efficiency of wireless communication networks. Particularly, for all messages concerning the network attachment (i.e. L3 messages) a radio bearer has to be established between the MN and the network. This requires the establishment of expensive traffic channels.
In FIGS. 5 and 6 a part of a cellular wireless communication network is shown for illustrating different Neighbor Discovery situations. In general, when the MN is for example L2 dormant (i.e. a state in which the MN restricts its ability to receive normal IP traffic by reducing monitoring of radio channels, which allows the MN to save power and reduces signaling load on the network), it “wakes up” after specific periods of time to perform periodic routine functions, for example to monitor paging channel (PCH) and for periodic L2 updates depending on the CELL_PCH or the URA_PCH (URA: UTRAN Registration Area) dormancy levels. However, every time it performs an L2 update, for radio efficiency reasons, the AP must also send (or allow from AR) the L3 network information to provide the current network attachment information, like the Router Advertisement. If the information is different from current network attachment in the MN, the MN obtains a new CoA and performs MIPv6 Binding Updates to all the mobility agents like HA and/or MAP (if HMIP is used).
Referring to FIG. 5, we assume a case where MN (i.e. MN1) has a network attachment (CoA) previously from an AR (in FIG. 5, AR1). That means, that the original Cellular Access Point CAP1 has provided the MN1 with the Router Advertisement of AR1, and the MN has a CoA from AR1 and performs a corresponding binding update for mapping this CoA at its HA. Thereafter, e.g. after a specific period of time, the MN1 may go L2 dormant. The MN1 can become L2 dormant in either cell level (CELL_PCH) or RRA (Radio Resource Allocation) level (URA_PCH). When the MN1 moves from one cellular Access Point CAP1 to another CAP2, as shown in FIG. 5, if it is in the CELL_PCH dormant state, it will perform cell updates. At the same time, the new CAP2 must allow the MN1 to receive a Router Advertisement to check its latest network attachment. In the case that the new CAP2 belongs to a different AR (not shown) a different network prefix is sent and an attachment procedure is performed. However, in the other case, in which the new CAP2 belongs to the same network coverage as the previous CAP1 to which the MN1 was associated before (as shown in FIG. 5), there is also established a Radio Bearer to provide the MN1 with the Router Advertisement (i.e. the prefix of AR1). The same situation applies to URA_PCH state, only that the MN wakes up only when it changes the cells at the RRA level, while the rest of the procedure remains the same.
In a more complex network scenario, such as shown in FIG. 6, where there may be many-to-many relation between different CAP (CAP1, CAP2) and AR (AR1, AR2, AR3), the situation becomes also more complex. Again, MN1 is provided with the Router Advertisement of AR1 by the CAP1, has performed the binding update, and may be gone to L2 dormant state. When the MN1 moves from its original CAP1 area to a new CAP2 area, the CAP2 could theoretically selectively provide one (or more) optimum Router Advertisements to the MN1. However, due to efficiency reasons, the CAP2 is not adapted to provide Router Advertisements from every AR it is connected to. Thus, the new CAP2 selects one of the connected AR (e.g. AR3) of which the Router Advertisement is sent to the MN1, which in turn performs the described attachment procedure.
This existing scheme is in particular problematic with regard to radio resources. As described above, for the provision of the network attachment information (L3), a Radio Bearer has to be established. In the case of FIG. 5, it is actually unnecessary for the MN to receive the Router Advertisements of the AR1. The problem is not just to send the Router Advertisement, but also to send it over the default Radio Bearer, which must be established if the MN1 was L2 dormant. In the case of FIG. 6, even though the CAP2 also belongs to the same AR that the MN was originally connected to (i.e. AR1), the CAP2 must provide a new Router Advertisement from any of AR1, AR2 or AR3 after establishing a new default Radio Bearer. The problem amplifies when the MN receives the new Router Advertisement, for example, of AR3. Then MN1 has to reconfigure a new CoA and perform all the MIPv6 binding procedures, while there was actually no need for this. Thus, this mechanism is a drain on the MN power and also very inefficient on radio resources.
One approach to reduce the signaling load in IP based communication networks is the so-called IP Dormancy/Paging, which is described, for example in IETF RFC 3154 and RFC 3132. However, this approach is still vague and will increase the network complexity of the network due to the involved paging network architecture.